The present invention relates to a plant for storing gas under pressure. The plant is especially suitable for storing compressed gaseous hydrogen and can be connected a hydrogen fuel replenishment system. The invention can also be applied to other gases such as hydrocarbon compounds which are commonly stored for industrial purposes, for vehicle refilling or for heating purposes.
Gaseous hydrogen is typically stored in pressurized cylindrical tanks (pressure vessels) of various sizes. These cylinders are either made of steel or consist of composite material comprising a gas tight liner (typically metal or plastic) and a fibrous wrapper. A storage installation consists typically of several individual vessels, which are interconnected with gas tubing (gas supply tubing as well as gas discharge tubing). The vessels are typically arranged in a rectangular pattern and supported by a metal frame which keeps the vessels in position relative to each other and supports the entire bundle or stack of vessels. The axes of the vessels are oriented either horizontally (in one or more stacks) or vertically (in one or more bundles).
A storage installation is typically placed outdoors on or above ground level, sometimes housed in a light steel construction, or in a more solid concrete construction. Alternatively, the installation can be buried in earth below ground level providing improved protection from external influences such as radiation from adjacent fires or damage caused by explosions. This alternative is rarely used as it makes inspection of the vessels and interconnecting piping very difficult and requires expensive measures to prevent corrosion (such as for example coating of the external tank surface and/or installation of a sacrificial anode for cathodic protection).
To overcome the difficulties related to inspection of buried vessels while maintaining the safety features, a system for storage of liquid or gaseous hydro-carbon compounds has been proposed in NL-C-1001796. The vessels are submerged in a basin filled with a liquid, for example, water. Thus, the vessels are protected from external influences such as fires and explosions while the vessel can be easily inspected by lowering the water level in the basin. Optionally, the top of the basin can be covered with wood, steel or concrete elements.
The above system however, makes gas leak detection difficult. The system will allow gas leaks to penetrate uncontrolled through the top of the basin, thus posing an inherent risk of undetected explosive gas mixtures.